When several vertical lathes are arranged next to one another to perform the successive machining of identical parts, the workpieces themselves are transferred from one lathe to the next one by so-called portal apparatuses equipped with manipulators movable on horizontal and vertical axes. The operation of these loading and unloading apparatuses is controlled by a computer which dialogues with the lathes. All of these means, intended for feeding and unloading the workpieces from a series of vertical lathes in a cascade arrangement, involve considerable purchase, maintenance and, not least of all, operating costs since the presence of highly qualified personnel is required.